This invention relates to a method for applying an atmosphere purifying catalyst to a heat exchanger and more particularly to a method for applying a manganese oxide ozone depleting catalyst to vehicular radiators and like heat exchangers.
Ozone treating catalyst compositions are well known in the art. Such compositions include manganese oxides, especially manganese dioxide alone or in combinations with copper oxide and aluminum oxide. Precious metal-containing materials are also known to decompose ozone. Reference can be had to assignee""s U.S. Pat. Nos. 5,422,331 and 6,340,066 and assignee""s PCT publications WO 00/13772; 00/13773; and 00/13790, all of which are incorporated by reference herein so that details relating to the composition and formulation of the ozone depleting catalyst need not be set forth in detail herein. The compositions of the manganese oxide catalysts as shown by these references have been developed and refined to the extent that thin layers of the catalyst can adhere to metal substrates subject to vibrations encountered in a vehicular application.
The prior art has recognized the benefit of applying air purifying catalysts and the like on moving vehicular heat exchange surfaces (such as those formed on vehicular radiators, oil coolers and air conditioning units) for purifying the atmosphere. See German Patent No. DE 40 07 965 C2. See also, U.S. Pat. No. 3,738,088 and the ""066 patent. While the published prior art clearly discloses that vehicular heat exchangers, specifically radiators, can be coated with a manganese oxide ozone depleting catalyst, there is little published literature teaching how such coating is to be applied.
The primary purpose of a vehicular radiator or any vehicular air-to-liquid heat exchanger is to effectively cool the liquid coolant circulating through the heat exchanger. As is well known, liquid coolant circulates through tubes which have corrugated foil or fins between adjacent tubes through which cooling air flows. The fins have thin slits, or louvers, punched therein at a precise angle to enhance cooling. If the spaces between fins or the louvered openings are closed by the coating the radiator cannot achieve its design efficiency.
At the same time, governmental agencies have recently recognized the benefits to the environment which can be achieved by moving vehicles equipped with ozone depleting catalysts (as well as other atmosphere purifying catalysts). Accordingly, some governmental agencies have, or are, contemplating extending environmental credits to automobile manufacturers who have equipped their vehicles with ozone depleting catalysts which may be used to offset certain polluting emissions produced by the vehicle""s internal combustion engine. The credits are or will be based on the total heat exchange area of the radiator or other heat exchange device. Thus, to achieve maximum environmental benefit for the catalyst coated heat exchanger, the entire heat exchanger area is to be coated with the ozone depleting catalyst. At the same time, the coating cannot be applied in a manner which could clog very small spaces within the radiator necessary for the radiator to achieve its cooling capacity.
The assignee has developed a system for coating vehicular radiators with a manganese oxide ozone depleting catalyst which has produced commercially acceptable radiators coated with an ozone depleting substance. The system is diagrammatically illustrated in prior art FIG. 1 and resembles an automated vehicular paint line. A robotic arm 1 carries a spray head 2 and moves the spray head in a horizontal, vertically indexed spray pattern. A peristaltic pump 3 is connected to a manganese oxide slurry vat 4 which is agitated and valved into communication with spray head 2. Spray head 2 also receives pressurized air 5 to produce an atomized slurry spray directed against one face side of the radiator. The system is a recirculating system as shown. When the slurry is not being pumped to the spray head 2 it is recirculated to the slurry vat 4.
In the overall process, the radiators are initially identified, initially weighed and cleaned in a power wash station 6. The radiators are then dried and again weighed at drying station 7. The radiators are now ready for coating. Because the manufacturers do not desire the frame to be coated for any number of reasons (for example, assembly fit or aesthetics) and the frame does not xe2x80x9cseexe2x80x9d air flow (and consequently does not deplete ozone), the radiator frame is masked at station 8 so that only the radiator window containing the tubes and fins is exposed. Masking typically has been accomplished by tape, although in some instances fixtures or grippers blocking off the frame or certain portions of the frame (in combination with the tape) have been used. The radiator fin window is then sprayed at station 9 on one face after aligning the radiator in a fixture. An air knife follows the spray to assure penetration of the slurry at least to the center of the radiator core. The radiator is rotated 180xc2x0 to expose the opposite face, aligned and sprayed in the horizontal sweep vertically indexed pattern to coat the radiator fin window on the opposite face. The radiator is then dried and weighed at station 10. Weight increase is attributed to catalyst deposition and checked against a desired catalyst loading range. The assumption is that the catalyst has been uniformly dispersed throughout the surface area of the radiator fin window. The system as described works and successfully coats radiators.
This invention is directed to improvements in the ozone depleting catalyst spray system as described above which increases throughput, improves coating consistency and assures system repeatability.
This feature of the invention is achieved in a method for applying an ozone depleting coating of manganese oxide to a vehicular radiator having a frame, a plurality of tubular conduits within the frame for carrying a coolant and corrugated foil or fins between the conduits having louvers formed therein. The method includes the steps of providing an agitated vat containing a slurry of manganese oxide. Also provided is a plurality of spray heads mounted in spaced relationship on a robotic arm that is movable relative to the radiator. Each spray head is provided with a source of pressurized air regulated by flow and/or pressure when valved into fluid communication with any given spray head. The method provides that for each spray head, a separate peristaltic pump for pumping the slurry from the vat to an associated spray head is utilized with each pump independently controlled to operate at a generally constant speed. The pressurized air and the slurry from the peristaltic pumps are independently valved into fluid communication with the spray heads to produce an atomized, fan-shaped slurry spray from each spray head and the valving step is maintained for a set time sufficient to allow the robotic arm to complete a set movement pattern for spraying one face side of the radiator with the slurry penetrating to at least the center of the fins. The valving for the set time is then repeated for spraying the opposite face side of the radiator whereby the time to coat a radiator face side is reduced while the arrangement of a separate peristaltic pump for each spray head assures a consistent catalyst loading applied to the surface area of the radiator.
In accordance with another aspect of the invention, one of the spray heads is set to produce an elliptical spray pattern and the robotic arm is programmed to move the elliptical pattern spray head in horizontal and vertical passes so that the spray head producing the elliptical spray pattern coats the peripheral edge of the radiator window without coating tanks, side or header plates while fluid communication of the slurry to the other spray heads is stopped whereby masking of the radiator is alleviated and catalyst waste is minimized.
In accordance with a more specific aspect of the invention, the spray pattern includes programming the arm movement to index the spray heads vertically up or down at the completion of a horizontal sweep of the arm. The horizontal sweep extends from a position adjacent one side of the window to a position adjacent the opposite side of the window and the spray pattern is generally conical with the vertical index step at least slightly less than the diameter of the spray pattern at the face surface (spray plume) of the radiator. The plurality of the spray heads include at least a first and second spray head with the second spray head positioned at a set distance below the first spray head and the indexing steps continue until one of the spray heads is vertically indexed to the vertical position occupied by the other spray head at the start of the spray cycle.
In accordance with yet another aspect of the invention, because the method uses a dedicated peristaltic pump for each spray head, select pumps are valved into fluid communication with their associated spray heads or out of fluid communication with the spray heads whereupon the pump slurry is returned to the slurry vat without adversely affecting catalyst loading on the radiator. Accordingly, any number of arm movements correlated with independent control of select spray heads can be programmed into the method to permit a large number of different radiator sizes, designs and configurations to be efficiently coated with the manganese oxide catalyst using one arm with multiple spray heads.
In accordance with the invention""s broader scope, an improved method of spraying any catalyst in slurry form onto an object is provided.
In general summary, the invention is an improved ozone depleting catalyst spray system for vehicular heat exchangers which has one or more, or any combination, of the following:
A) higher throughput;
B) consistency in coating applied to radiator window;
C) minimal catalyst waste;
D) independent spray head control for enhanced versatility;
E) elimination or minimizing masking; and/or,
F) repeatability or robustness in system operation.